Tuesday, February 14, 2017

Roast Phases, Statistics and Phases LCDs

The coffee roasting process is often discussed with respect to its separate roasting phases. Splitting not only makes it easier to get complex things into our small heads, but also allows for colourful roasting graphs.

Roast Phases

Often roast masters identify distinct roast phases.

  • Drying: from heating the beans to the point where the beans turn yellow (DRY)
  • Maillard: from DRY to the start of first crack (FCs)
  • Finishing: from FCs to the end of the roast (DROP)

Artisan marks the drying phase in green, the Maillard phase in yellow and the finishing phase in brown. Note that in versions before v1.0 the last phase was called "Development", but we got convinced by a number of discussions (thanks Susan;) that the actual roast development starts way before the FCs. Thus we have chosen the neutral "Finishing" for the last phase.

The three coloured watermarks (green/yellow/brown) featured on the main window of Artisan have been around since its initial release v0.1 in 2010. Those colors made Artisan easily recognisable on computer screens around the world (until those watermarks, with the exact same colors, were copied in 2013 by the RoastLogger app).

The temperature limits of each phase can be configured in the phases dialog (menu Config >> Phases). One can define two sets of phases limits (randomly called Filter and Espresso) to quickly switch between two sets of limits.

In the lower part of this dialog, a number of flags configure the behaviour of Artisan w.r.t. the roast phases. Either you let the phase limits be adjusted automatically based on the roasting events ("Auto Adjusted" flag ticked), or you decide to keep the phases limits fixed as defined in this dialog ("Auto Adjusted" flag unticked). In the latter case, you make tick "Auto DRY" and/or "Auto FCs" to let Artisan automatically issue the corresponding events during a roast as soon as the bean temperature (BT) reaches the corresponding pre-defined phase limit. Finally, in case you think those coloured watermarks are disturbing, you can untick the "Watermarks" flag to hide them away.


On completed roasts, Artisan calculates certain statistics per roast phase. The absolute time and relative time portion together with the average rate-of-rise (RoR) in C/min or F/min per roasting phase is displayed in the statistic bar on top of a roast profile (only visible after a completed roast). The relative temporal size of the finishing phase is also known as Rao's development time (here 20%).

There is the bean cooling phase drawn in blue as the final phase starting from the dropping of the beans into the cooling bin (DROP) until the roasted beans reached room temperature (COOL).

Changing the flags in the statistics dialog (menu Config >> Statistics) allows to display different information per phase, like the AUC or an evaluation based on time limits per phase.

If the Characteristics flag is ticked in that dialog, the basic information on the roast, like date, time,. beans, batch-size, roast-loss, and color are given as x-axis label.

A right click on that x-axis label toggles this characteristics bar into a second mode, displaying some more technical roast informations, like the MET (maximum ET temperature), total RoR and total AUC.

Phases LCDs

While the roast statistics discussed above are only available after a roast, some important information is handy to have it calculated during the actual roasting, like the development ratio.

If the Phases LCDs flag in the phases dialog (menu Config >> Phases) is ticked, three small LCDs are displayed on top border of the main window, one per roasting phase.

Each of those LCDs displays information relative to the current progress of the roast and operates in one of three modes: time / percentage / temperature.

For example, in the following situation, the roast just passed the turning point (TP) and is approaching DRY. The phasesLCDs are in time mode. The TP lcd indicates that 2:45 minutes have passed since TP and that, based on the current RoR, DRY is expected to happen 7:41 minutes into the roast. The last LCD does not have any meaningful information to be displayed yet.

A little bit further into that roast, we just passed DRY (39 seconds ago as reported by the second LCD and 6:15 minutes after TP) and are approaching FCs. Now the last LCD reports that the FCs is estimated to happen at 11:08 minutes into the roast. Additionally, a small number between the TP and the DRY LCD tells us that DRY happened exactly 5:36 minutes after TP.

Finally, 21 seconds ago we reached FCs at 11:51, 4:21 minutes after DRY.

Now it would be good to know the ratio of this last phase w.r.t. the total roast time to be able to stop the roast at e.g. 20% development ratio. Just clicking the phases LCDs with the right mouse button switches from time to percentage mode, and we see that we still have some time as we are only at 3% right now.

Another right-click on the phases LCDs toggles from percentage into temperature mode, indicating the temperature difference relative to the previous roasting event. This might be useful if we want to stop our roast e.g. 10C above FCs.